A fourth attacker may have been involved in a suicide bomb attack on an Israeli tourist bus in Bulgaria two years ago, the country’s chief prosecutor said Thursday.

The July 2012 explosion outside an airport on Bulgaria’s Black Sea coast killed five Israeli tourists, the Bulgarian bus driver and the bomb carrier, who has never been identified. Thirty-five people were wounded. Bulgaria already has identified two suspects, both of Lebanese origin, but neither has been arrested.

The prosecutor, Sotir Tsatsarov, said Bulgaria’s plans to press formal charges against the two men by March would need to be delayed because investigators have identified a third man suspected of involvement in planning the attack. He declined to detail the man’s identity or nationality.

“This does not mean that the indictment (of all three suspects) will be postponed indefinitely, but we will need some additional time,” Tsatsarov said.

Last year Bulgaria accused the Lebanese militant group Hezbollah of mounting the attack. It identified two Lebanese plotters as Meliad Farah, 32, who holds Australian citizenship, and Hassan El Hajj Hassan, 25, a Canadian citizen. The third suspect, the bomber, was decapitated in the blast. DNA and fingerprint analysis produced no identification matches.

Bulgaria previously has complained that Lebanon had not provided assistance in identifying the whereabouts of either man. Tastsarov said Thursday its diplomatic requests remain unanswered. Partly in response to the bombing, the 28-nation European Union unanimously decided to declare Hezbollah’s military wing a terrorist organization.

(AP)